In the feeding of a sheet metal web or strip from a supply coil into a mechanical reciprocating press, the supply coil is usually supported by a pay-off reel, and either the coil is driven in an unwinding direction by a variable speed hydraulic motor or the strip is pulled from the coil by a set of driven pinch rolls such as used on a strip straightening device. A loop is formed within the metal strip between the supply coil and a stock feeder which is operated in timed relation with the reciprocating press and advances the strip into the press in predetermined increments. Commonly, the motor which unwinds the supply coil is controlled by either optical or sonic detectors which detect vertical movement in the bottom of the loop. When the bottom of the loop moves up, the unwinding of the coil is automatically increased. One type of optical loop detectors or sensors is disclosed in U.S. Pat. No. 4,447,016 which issued to the Assignee of the present invention.
When a large supply coil is used, for example, a coil weighing 25,000 pounds or more, the rotating coil has substantial momentum which can result in producing problems in obtaining precision incremental feeding of the strip into the press by the stock feeder. For example, substantial variation in the loop results in significant changes in the weight of the strip forming the loop, and these changes and/or jerking of the loop result in substantial variations in the tension within the strip ahead of the stock feeder. This change in tension makes it more difficult for the stock feeder to obtain precision feeding of the strip, especially when the speed of the press and stock feeder are increased to obtain maximum production from the press.